SailNet Community - Reply to Topic
Thread: High Output Alternators Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

  Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below

  Topic Review (Newest First)
10-13-2004 12:16 PM
High Output Alternators

I was crusin this summer and I bought a new battery bank three batteries and an alt.
the batteries were two AMG 31 and a led acid 31 I know they should be the same but the led acid is isolated and not the house. Anyway I bought a Balmar with the brain it is an expensive little bugger,the problem with it is it never worked I left port and while it looked cool and showed voltage by that evening it was deadand so were my new batteries. Back on went the old 35 amp alt. I installed a disconnect on the cranking battery so I can put all the charg to the house batteries as the cranking bat needs very little charging. The Balmar may be very goog but why a company would make a system to charge only if the brain box works is beyond me it puts out no voltage at all without the box so if that dies so do your batteries. I returned the thing and have had no problems since and I went for almost two weeks without a dock.I am careful to always leave one battery full the cranking battery. The AMG batteries are great so far about three months old and holding well.
10-13-2004 01:10 AM
High Output Alternators

As Zeph said - yes & no.
There are several conditions that limit the output of an alternator, including: Altí Speed, and Batt. Acceptance.

Alternator speed is a function of engine speed and pulley ratio. Most Alternators are designed to provide full output at about 6,000 RPM, so you wonít get full output at anything under about 2,500 RPM engine speed (assuming 2:1 pulley ratio). Altí current output varies as the inverse of the square of speed - so a 35 A rated (@ 6,000 RPM cold) alternator, turning at 4,000 RPM (66%) will only put out a maximum of about 15 Amps (0.66 x 0.66 = 0.4356%) & (35A x 0.4356 = 15.246 A).

Acceptance rates vary proportionally with battery size. A larger battery (more A/H capacity) will accept more charging current. A small battery bank will not benefit (much) from a High Output alternator.

10-12-2004 03:43 PM
High Output Alternators

In a word - yes. In another word - no. (Sorry, I just had to do that tonight!) If you don''t care how long it takes to recharge your batteries (because you only use them a little bit and then put them back on a shore power charger) then the answer is no - there is no need for a high output alternator. The more complete answer is - the output of the alternator needs to be matched to the size of the battery bank + the load you run during charging (e.g. navigation lights, helm instruments such as wind, speed, depth, radar, chart plotter; refigeration) + the amount of time you are willing to run the engine to charge the batteries + any other potential charging sources (e.g. Wind, Solar, Towed Generator.) Replacing the charge of 50% of a 50 amp hour battery bank takes a lot less time than replacing the charge of 50% of a 2000 amp hour battery bank. So you are really juggling four parameters: output of the alternator, size of the battery bank, how much of the alternator output is not available for charging as it is running other things and how much you deplete the charge on the battery bank.

Confession: Someone responded to one of my posts with the suggestion that I check out Nigel Calder''s Boatowner''s Mechanical and Electrical Manual (second edition.) Well, you know, I''m a guy and a trained engineer and have owned boats for years - what would be the point? But I took it out from the library and it is fantastic. Read Chapter 1 on "Establishing a Balanced Battery-Powered Electrical System. You will be glad you did.

Fair winds and following sea.
10-12-2004 01:05 PM
High Output Alternators

Can someone help me clarify some issues surrounding high output alternators? I''m not sure I see the logic in having one unless one does a lot of extended cruising where your battery bank is discharged by more than 50%. It seems with three stage chargers, the charging rate is almost always in the range of 15 to 30 amps. If that is the case, the standard 35 amp alternator should be fine.

The only time I can see when a high-output alternator is when the batteries are down at the 50% level. At that point, you might get at higher charge rate. So - if you are off crusing somewhere and cycling the batteries between 1/2 capacity and 3/4 full, you will need to run the engine less. But for someone who doesn''t deplete the batteries below 3/4 full charge - I don''t see it making sense.

Hope that was clear...

Do I have it right?


Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

For the best viewing experience please update your browser to Google Chrome